Hulling machines used heretofore have not achieved particularly efficient results, as the resulting kernels are usually mixed with some 15% hulls, or non-hulled (whole) seeds. The separated hulls contain some 3 to 5% small pieces of kernel, which is a loss of significant value.
Also, such a high percentage of hulls in the kernels increases milling costs and reduces milling capacity, as a greater volume must be processed to obtain the same volume of dehulled kernels.
Considering further that once the oil is extracted the remaining pulp (solid) is the base for balanced animal feeds, and as hulls contain a high percentage of fiber, which is very harmful to non-ruminants and specially to chicks, it appears clearly there is a need to better the process and to decrease the hull percentage in the kernels that go to pressing, extraction, etc.
Another factor militates against the efficiency of the process, namely the absorption of oil by the separated hulls, which is most difficult to recover and constitutes an important loss. This is especially true when using hulling machines of the fixed-and-rotating-blades type; as many kernels are cut in pieces, they expel some of their oil, which particularly wets the hulls.
An attempt has been made to improve hulling machinery in which seeds are thrown against hardened surfaces and--taking advantage of the special configuration of sunflower seeds which present two substantially symmetrical "hulls" (with respect to a central plane) and a "weld" around the perimeter--impact against the hardened surface which causes the hulls to break along the weld or fault line, the kernel falling out.
But, in the impact system not all seeds are broken or hulled on impact since this depends on the position of the seed at the moment of impact if the seed impacts with one of its lateral faces or sides, the probability is that it will not break. All non-hulled or whole seeds must be separated and reprocessed with obvious disadvantages.
The above is further complicated by the fact that, as rotors spin at high velocities to achieve sufficient centrifugal force, many seeds, kernels and their pieces, rebound into the path of new seeds ejected from the rotor, this of course impedes a correct action with the result of more unhulled seeds and a further loss of efficiency.